Fluid compositions containing an



FLUID COMPOSITIONS CONTAINING AN ORTHOSILICATE Robert L..Merker, Bellevue, Pa., and William A. Zisman, Washington, D. C.

No Drawing. Application June 18, 1953, Serial No. 362,696

9 Claims. (Cl. 252-40.7)

(Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates to new fluid compositions having lubricating properties, more particularly to improved aliphatic ester oils and greases.

The aliphatic ester oils to which reference is made herein and with which the present invention is concerned are liquid saturated aliphatic normal esters of saturated aliphatic carboxylic acids which esters are further defined by the fact that their boiling point is 150 C. or higher. This class of liquid aliphatic esters has been recognized by the art as a source of synthetic lubricating oils and some of these esters have been used with metal soaps for making greases. The art is also aware that metal soaps accelerate the thermal oxidation of these liquid aliphatic esters and has added antioxidants to the greases to improve their oxidation stability.

The present inventionas has an object the provision of a new class of antioxidants for improving the oxidation stability of the aliphatic ester oils which contain metal soaps, especially at elevated temperatures. A further object is the provision of aliphatic ester oil greases which have enhanced oxidation stability at elevated temperatures. Other objects will appear hereinafter from the description of the invention.

We have found that the oxidation stability at elevated temperatures of aliphatic ester oils which contain metal soaps can be improved by the addition thereto of small amounts of an orthosilicate which is aromatic or hydroaromatic or mixed aromatic-hydroaromatic in character. The orthosilicate antioxidants of the present invention contain an aromatic or hydroaromatic group on each of at least two of the ester oxygen atoms of the molecule, with a lower alkyl group being attached to such of the ester oxygen atoms as are not satisfied by an aromatic or hydroaromatic group. These orthosilicates have the general formula:

R-O O R2 S1 R1O/ ORa wherein R, R1, R2 and R3 each represent an aromatic or a hydroaromatic radical, or in part represent a lower alkyl radical of up to 6 carbon atoms where only two or three of the ester oxygen atoms of the orthosilicate molecule are attached to an aromatic or hydroaromatic radical. The radicals R, R1, R2 and R3 may be the same or different aromatic and hydroaromatic groups and the same or difierent lower alkyl groups where two such are present in the orthosilicate molecule. The radicals R, R1, R2 and R3 may be aryl or hydroaryl groups which may be substituted or not by groups such as, for example, alkyl, cycloalkyl, aralkyl, alkoxy, aryloxy, hydoxy, carboxy, carbalkoxy, nitro, amino, alkylamino, arylamino, etc., groups. Thus, the aromatic radical of the ortho-silicates may be, for example, phenyl, naphthyl, diphenyl, tolyl, xylyl, cyclohexylphenyl, benzylphenyl, anisyl, phenoxyphenyl, hydroxyphenyl, carboxyphenyl, carbethoxyphenyl, nitrophenyl, aminophenyl, N-methyli d States Patent 9 1 aromatic radical of the orthosilicates may be, for exby weight.

ample, cyclohexenyl, cyclohexyl, decalyl, tetralyl, methylcyclohexyl, dicyclohexyl, phenylcyclohexyl, benzylcyclohexyl, hexahydroanisyl, phenoxycyclohexyl, hydroxycyclohexyl, carboxycyclohexyl, carbethoxycyclohexyl, nitrocyclohexyl, aminocyclohexyl, N-methylaminocyclohexyl, N-phenylaminocyclohexyl, etc., groups. Where the group attached to the oxygen atom of the orthosilicate molecule is a lower alkyl radical the same may be, for example, methyl, ethyl, propyl, butyl, tertiary butyl, hexyl, etc. Illustrative orthosilicate compounds coming within the above general formula are, for example, tetraphenyl orthosilciate, tetra-o-tolyl orthosilicate, tetradiphenyl orthosilicate, tetra-B-naphthyl orthosilicate, tetracyclohexyl orthosilicate, di-methyl-di-phenyl orthosilicate, methyl-tri-phenyl orthosilicate and ethyl-tri-o-tolyl orthosilicate.

A preferred class of the orthosilicate compounds as antioxidants for the new fluid compositions are those in which the aromatic and hydroaromatic groups are attached to the ester oxygen atoms of the orthosilicate molecule are monoor dinuclear and more preferably are monoand dinuclear aryl and hydroaryl groups which may or may not contain lower alkyl groups, for example, methyl, ethyl, isopropyl, butyl, tertiary butyl, hexyl, etc., groups. Within this preferred group of orthosilicate compounds is to be mentioned in partciular, tetraphenyl orthosilicate and tetracyclohexyl orthosilicate.

The stability to oxidation, especially at elevated temperatures, e. g. at to C., of the aliphatic ester oil-metal soap compositions can be enhanced by the addition thereto of one of the antioxidant orthosilicates in concentrations within the range of about 0.1 and 10% by weight therein, with a preferred general range for the addition of the antioxidant being from about 0.1 to 5% The amount of the antioxidant added will depend upon the activity of the individual orthosilicates and the particular aliphatic ester oil-metal soap composition. The orthosilicate compound is dissolved or dispersed in the aliphatic ester oil depending upon its solubility therein.

The aliphatic ester oils of the compositions of the invention may be prepared by complete esterification in known way between the corresponding saturated aliphatic carboxylic acids, for example, butyric, oxalic, adipic, 3- methyladipic, azelaic, tricarballylic acids, etc., and the corresponding saturated aliphatic alcohols, for example, methanol, 2-ethylhexanol, ethyleneglycol, glycerol, pentaethrythritol, etc.; the acids and the alcohols being selected so as to obtain the desired liquid normal ester as will be understood by those skilled in the art. A class of esters of particular interest for the compositions of the present invention are the liquid saturated aliphatic diesters of the saturated aliphatic dicarboxylic acids which.

have an alkylene chain of 3 or more carbon atoms, more especially those which are straight or branched chain alkyl diesters of the 5 to 12 carbon atom alkylene dicarboxylic acids in which the alkylene chain may be branched or unbranched and which have the general formula:

ethylhexyl azelate, di-Z-ethylhexyl sebacate, di-(3,5,5

3 trimethylhexyl) sebacate, 2,4-pentanediol dihexanoate, triamyl tricarballylate, pentaethryritol tetrahexanoate, etc. The metal soap in the compositions of the invention may be any of the metal salts of the soap-forming fatty and hydroxy fatty acids, for example, the calcium, strontium, barium, sodium, potassium, lithium, copper, tin,

lead, zinc, aluminum, etc., salts of lauric, myristic,

palmitic, oleic, ricinoleic, stearic, arachidic, behenic, erucic, 12-hydroxy stearic acid, etc., or of mixtures of these acids. The amount of the metal soap in the compositions may be widely varied and range from as little as about 0.1% by weight up to a practical maximum. In the case of lubricating greases, the metal soap content of the compositions will generally be from about to 30% by weight, for which usually there is employed one of the alkaline earth or alkali metal soaps, for example, calcium, strontium, barium, sodium and lithium stearates.

The invention is illustrated in greater detail by the following specific examples in which the orthosilicate compound was incorporated in a lithium soap-diester grease and subjected to an accelerated oxidation test to determine its efiicacy as an antioxidant for the metal soap-diester oil composition at elevated temperatures. The greases were prepared in conventional manner by heating the aliphatic ester oil and metal soap together under stirring to form a clear solution, quickly cooling the solution to form a gel and working the gel through a screen to obtain a grease of uniform consistency (about workings through a Hain Microworker). The antioxidant was mixed into the grease and the whole then worked through the screen as before to obtain uniformity of admixture. The control grease or blank was made up to contain the same relative proportion of the metal soap and diester oil in each instance but without the presence of the orthosilicate anti-oxidant. The accelerated oxidation tests were carried out in accordance with Navy Specification ANG-3a(2) using a Norma-Holiman bomb apparatus.

Example 1 A grease was prepared to contain 16.2 mol percent (11.12% by weight) lithium stearate, 80.8 mol percent (87.68% by weight) di-Z-ethylhexyl sebacate and 3.0 mol percent (1.2% by weight) tetraphenyl orthosilicate. A control grease was made up in the same manner to contain only lithium stearate and di-Z-ethylhexyl sebacate in the same relative proportions.

Twenty gram samples of each of the two greases were placed in separate Norma-Hoffman bombs which were then sealed, heated to 100 C. and oxygen pressed thereinto at 110 pounds per square inch. The oxidation test was run for a period of 300 hours during which time the temperature in bombs was maintained at 100 C. L0.5 C.

Bomb pressure readings were made at intervals over the 300 hour period, which readings were accurate to :10 p. s. i. Consumption of oxygen by the grease and thereby oxidation of the same is indicated by drop in the oxygen pressure in the bomb. Readings of the pres sure in the bomb containing the control grease showed a rather sharp drop even in the earlier stages of the run (up to 50 hours) which was progressive until at the end of the 300 hours, the pressure stood at 50 pounds per square inch, indicating a substantial amount of oxidation to have taken place in the unprotected grease. On the other hand, pressure readings in the bomb containing the grease to which the tetraphenyl orthosilicate had been added showed no drop in pressure over the 300 hour period, indicating the orthosilicate compound to be a particularly effective antioxidant for the grease.

Example 2 The oxidation test of Example 1 was applied concurrently to a like grease containing 3 mol percent tetracyclohexyl orthosilicate in place of the tetraphenyl orthosilicate, using the same constant temperature bath to heat the bomb. Bomb pressure readings showed only a very small drop in pressure over the period of 300 hours, approximately 2 to 3 p. s. i., indicating the tetracyclohexyl orthosilicate to be also a particularly effective antioxidant for the grease.

Example 3 A grease was made up to contain 12% by weight lithium stearate, 3.2% by weight tetraphenyl orthosilicate and the remainder di-Z-ethylhexyl sebacate was subjected to the like oxidation test as in Example 1 but at a temperature of 150 C., and for a period of 20 hours. The grease containing the tetraphenyl orthosilicate showed an 8.0 p. s. i. drop in oxygen pressure after 20 hours whereas the control for the same period showed a drop of 57 p. s. i. oxygen pressure, indicating the orthosilicate compound to be an effective antioxidant for the grease at 150 C.

The aliphatic ester oil-metal soap compositions of the present invention maybe blended with miscible proportions of other lubricating oils, such as petroleum oils and polyoxyalkylene oxides having one or both terminals ending in an alkyl other group, e. g., the butoxy group. Antioxidants of types other than the orthosilicates may be used in the compositions in conjunction with the tetraaromatic and tetrahydroaromatic orthosilicate antioxidants, such as phenolic and aromatic amine type antioxidants which are active as antioxidants at the lower temperatures, e. g. below C., and thereby will impart supplemental protection to the aliphatic ester oilmetal soap compositions at temperatures occurring during storage or during other low temperature nonoperating periods, e. g., cyclohexyl phenol, p-hydroxy diphenyl, 4-t-butyl-Z-phenylphenol, thymol, catechol, phenyl-anapthylamine, etc. Other antioxidant compounds of the non-silicate type are dialkyl selenides, e. g., dilauryl selenide, and phenothiazine. Some of these supplemental antioxidant compounds are active, at the elevated temperatures also, for example, dilauryl selenide and phenothiazine.

While in the foregoing description we have made reference to certain specific embodiments of the invention, these are intended by way of illustration and not in limitation since the invention may be variously embodied without departing from the spirit or scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What we claim is:

1. A fluid composition comprising a liquid saturated aliphatic normal ester of a saturated aliphatic carboxylic acid, which ester has a boiling point not lower than C., a metal. soap, and a small amount of an orthosilicate of the general formula:

wherein R, R1, R2 and Rs are selected from the group consisting of lower alkyl radicals having up to 6 carbon atoms, aromatic and hydroaromatic radicals and at least two of the same are selected from the group consisting of aromatic and hydroaromatic radicals.

2. A fluid composition as defined in claim 1, wherein the liquid ester is an alkyl diester of a saturated aliphatic dicarboxylic acid.

3. A fluid composition as defined in claim 1, wherein the liquid diester is a branched chain alkyl diester of a saturated dicarboxylic acid.

4. A fluid composition comprising a liquid branched chain alkyl diester of a saturated aliphatic dicarboxylic acid, which ester has a boiling point not lower than 150 C., a metal soap and a small amount of a tetraaryl orthosilicate.

5. A grease composition comprising a liquid branched chain alkyl diseter of a dicarboxylic acid of the formula:

wherein R1 is a bivalent aliphatic hydrocarbon radical of from 3 to carbon atoms, which ester has a boiling point not lower than 150 C. and is thickened with a metal soap selected from the group consisting of alkaline earth and alkali metal soaps, and a small amount of a tetraaryl orthosilicate.

6. A grease composition as defined in claim 5, wherein the tetraaryl orthosilicate is tetraphenyl orthosilicate.

7. A fluid composition comprising a liquid branched chain alkyl diester of a saturated aliphatic dicarboxylic acid, a metal soap and a small amount of a tetrahydroaryl orthosilicate.

8. A grease composition comprising a liquid branched chain alkyl diester of a dicarboxylic acid of the formula:

HOOCR4COQH wherein R4 is a bivalent aliphatic hydrocarbon radical of from 3 to 10 carbon atoms, which ester hasa boiling point not lower than C. and is thickened with a metal soap of the group consisting of alkaline earth and alkali metal soaps, and a small amount of a tetrahydroaryl orthosilicate.

9. A grease composition as defined in claim 8, wherein the tetrahydroaryl orthosilicate is tetracyclohexyl orthosilicate.

References Cited in the file of this patent UNITED STATES PATENTS 2,053,474 Graves et al. Sept. 8, 1936 2,129,281 Lincoln et al. Sept. 6, 1938 2,181,914 Rosen Dec. 5, 1939 2,242,400 Loane et al. May 20, 1941 2,335,012 Johnston Nov. 23, 1943 2,383,605 Lieber et al. Aug. 28, 1945 2,436,347 Zimmer et a1. Feb. 17, 1948 2,643,263 Morgan June 23, 1953 OTHER REFERENCES Fitzsimmons et al.: Polyorganosiloxanes, Orgonosilanes, and Orthosilicate Esters as Antioxidant, published by Naval Research Labororatories. Copy in Oifice of Technical Information. 

1. A FLUID COMPOSITION COMPRISING A LIQUID SATURARED ALIPHATIC NORMAL ESTER OF A SATURATED ALIPHATIC CARBOXYLIC ACID, WHICH ESTER HAS A BOILING POINT NOT LOWER THAN 150* C., A METAL SOAP, AND A SMALL AMOUNT OF AN ORTHOSILICATE OF THE GENERAL FORMULA: 